There are several methods known as biometrics for recognizing or identifying an individual from personal biological characteristics. Some of these methods involve imaging of the face or eye and analyzing the facial features, retinal vascular patterns of the eye, or patterns in the iris of the eye. In recent years there has been a demand for more reliable systems to identify individuals, particularly those persons who desire access to a secured area or system. A common example of such a secured system is an automated teller machine which allows authorized users to conduct banking transactions. Many of these systems are used by a wide variety of people. Very often these people demand quick as well as accurate identification.
A technique for accurately identifying individuals using iris recognition is described in U.S. Pat. No. 4,641,349 to Flom et al. and in U.S. Pat. No. 5,291,560 to Daugman. In this method an image of an eye of a human is acquired, the eye is determined to be present at a selected location in the image, an iris portion of the eye is isolated, and an iris code is generated and compared to a previously generated iris code. The systems described in these references require clear, well-focused images of the eye.
One particular problem in acquiring a good image of the eye is the problem of locating the eye within a close-up image obtained by the camera of an imaging system. Many factors can degrade the performance of methods of locating the eye. The features of the human eye have considerable variation, sometimes causing difficulty in recognizing and isolating the iris. Subject movement during imaging causes blurred images. The small size of the eye causes difficulty at distances of only 1 to 2 feet. With present technology, it is very difficult to compute an accurate range via machine vision for precise focusing at a reasonable cost. For all of these reasons, multiple methods may be required to locate an eye in a close-up image with confidence. The present invention is one effective means of verifying a previously estimated location of an eye in a close-up image.